Question 985345
{{{(x+4)(x-9) = 4x}}}  expand the left side
{{{x^2 -9x +4x -36 = 4x}}} combine lie terms
{{{x^2 -5x - 36 = 4x}}} now solve
{{{x^2 -9x -36 = 0}}}
Now either factor of use the quadratic equation.
Let's factor
what two integers have the sum -9 and the product of -36?
How about -12 and 3?

{{{(x-12)(x+3) = 0}}}
For a product to equality zero, either one of both of its multiplicand or multiplier must be 0.
So either (x-12=0)  or (x+3=0)
That says x = 12 or -3

Now lets use the quadratic equation to solve
*[invoke quadratic "x", 1, -9, -36 ]

Either way, same result. Math is great!